This application generally relates to the field of finely directed fluid flow and more particularly to the creation of a stabilized capillary microjet which breaks up to form a monodisperse aerosol.
Devices for creating finely directed streams of fluids and/or creating aerosolized particles of a desired size are used in a wide range of different applications. For example, finely directed streams of ink for ink jet printers, or directed streams of solutions containing biological molecules for the preparation of microarrays. The production of monodisperse aerosols is also important for (1) aerosolized delivery of drugs to obtain deep even flow of the aerosolized particles into the lungs of patients; (2) aerosolizing fuel for delivery in internal combustion engines to obtain rapid, even dispersion of any type of fuel in the combustion chamber; or (3) the formation of uniform sized particles which themselves have a wide range of uses including (a) making chocolate, which requires fine particles of a given size to obtain the desired texture or xe2x80x9cmouth feelxe2x80x9d in the resulting product, (b) making pharmaceutical products for timed release of drugs or to mask flavors and (c) making small inert particles which are used as standards in tests or as a substrate onto which compounds to be tested, reacted or assayed are coated.
Although there is a need for creating finely directed streams of fluids and for creating small spherical particles which are substantially uniform in size current methods suffer from a number of disadvantages. The invention described and disclosed herein is based on new discoveries in the field of physics which make it possible to overcome disadvantages of prior art devices and methods in an energy efficient manner.
The invention is directed to a stable capillary microjet and a monodisperse aerosol formed when the microjet dissociates. A variety of devices and methods are disclosed which allow for the formation of a stream of a first fluid (e.g. a liquid) characterized by forming a stable capillary microjet over a portion of the stream wherein the microjet portion of the stream is formed by a second fluid (e.g. a gas). The second fluid is preferably in a different state from the first fluidxe2x80x94liquid-gas or gas-liquid combinations. However, the first and second fluids may be two different fluids in miscible in each other. The stable capillary microjet comprises a diameter dj at a given point A in the stream characterized by the formula:       d    j    ≅                    (                              8            ⁢                          ρ              1                                                          Π              2                        ⁢            Δ            ⁢                          xe2x80x83                        ⁢                          P              g                                      )                    1        4              ⁢          Q              1        2            
wherein dj is the diameter of the stable microjet, ≅ indicates approximately equally to where an acceptable margin of error is xc2x110%, xcfx811 is the density of the liquid and xcex94Pg is change in gas pressure of gas surrounding the stream at the point A.
The microjet can have a diameter in the range of from about 1 micron to about 1 mm and a length in the range of from 1 micron to 50 mm. The stable jet is maintained, at least in part, by tangential viscous stresses exerted by the gas on the surface of the jet in an axial direction of the jet. The jet is further characterized by a slightly parabolic axial velocity profile and still further characterized by a Weber number (We) which is greater than 1 with the Weber number being defined by the formula:   We  =                    ρ        g            ⁢              v        g        2            ⁢      d        γ  
wherein the pg is the density of the gas, d is the diameter of the stable microjet, xcex3 is the liquid-gas surface tension, and Vg2 is the velocity of the gas squared.
Although the Weber number is greater than 1 when a stable microjet is obtained the Weber number should be less than 40 to obtain a desired monodisperse aerosol. Thus, desired results are obtained within the parameters of 1xe2x89xa6Wexe2x89xa640. Monodisperse aerosols of the invention have a high degree of uniformity in particle size. The particles are characterized by having the same diameter with a deviation in diameter from one particle to another in a range of about xc2x13% to about xc2x130%, preferably about xc2x13% to about xc2x110% and most preferably xc2x13% or less. The particles in an aerosol will have consistency in size but may be produced to have a size in a range of about 0.1 micron to about 100 microns.
An object of the invention is to provide a stream of a first fluid (e.g. a liquid) which stream is characterized by forming a stable capillary microjet over a portion of the stream wherein this stable-capillary microjet portion of the stream is formed by a second fluid (e.g. a gas) moving at a velocity greater than that of the first fluid.
Another object of the invention is to provide a monodisperse aerosol of liquid particles in air wherein the particles are characterized by having the same diameter with a deviation in diameter from one particle to another in a range of from about xc2x13% to about xc2x130% wherein the particles are produced as a result of a break up of the stable capillary microjet.
An advantage of the invention is that the microjet of liquid flows through an opening surrounded by a focusing funnel of gas so that liquid does not touch the peripheral area of the opening and therefor does not deposit on the opening and cause clogging.
Another advantage of the invention is that the particles formed are highly uniform in size and are created with a relatively small amount of energy.
A feature of the invention is that various parameters including the viscosities and velocities of the fluids can be chosen with consideration to other adjusted parameters to obtain a supercritical flow of liquid which results in the formation of the stable capillary microjet.
Another advantage of the invention is that the positions of the liquid and gas within the various embodiments of the invention can be changed in order to obtain a variety of different effects. For example, when aqueous liquid forms a stable capillary microjet surrounded by a focusing funnel of gas which escapes into a surrounding gas at lower pressure, aerosolized particles are formed. In another example a flow stream of gas focused by a surrounding focusing funnel of liquid which flows outward into a liquid forms gas bubbles which are highly uniform and extremely small in size.
An advantage of the invention is that the embodiments can be used to form small gas bubbles which are uniform in size and sufficiently small to provide for a high degree of diffusion of the gas present in the bubble into the surrounding liquid, thereby providing advantages such as oxygenating water or decontaminating gas.
These and other aspects, objects, features and advantages will become apparent to those skilled in the art upon reading this disclosure in combination with the figures provided.